1. Field of the Invention
The present invention pertains to methods and apparatus for sampling fluids and, more particularly, to such methods and apparatus useful for sampling fluid discharged from the bottom of a downcomer pipe extending into a body of water from an offshore drilling platform.
2. Description of the Prior Art
Drill cuttings from offshore drilling operations are normally discarded to the sea floor from a single offshore platform during the drilling of a large number of wells. It is desirable that these drill cuttings be free from any petroleum based compounds. To remove oil from the drill cuttings before they are discarded onto the sea floor, it is conventional to pass the drill cuttings through a long, vertical pipe extending from the surface of the sea to a few hundred feet below the surface. This pipe is normally referred to as a downcomer pipe. As the drill cuttings are passed down through the downcomer pipe, the oil is washed from the drill cutting and floats toward the surface of the water in the downcomer pipe. The oil remains at the surface of the water and is occasionally skimmed off and pumped out. To ensure that the sea water is not being contaminated with oil, it is desirable to periodically sample the sea water near the bottom of the downcomer pipe. In the past, pumps have been placed in the downcomer pipe near the sampling location to deliver samples of the sea water to the surface. Unfortunately, the drill cuttings in the samples ruin the pumps and renders their operating lives extremely short and unreliable. Attempts to run conventional fluid samplers down the downcomer pipe have had the disadvantage that the oil and sludge near the surface of the water in the downcomer pipe completely coat the sample chamber and mix with the sample resulting in non-representative samples.
There are many other situations where it is desired to sample a fluid at a predetermined depth; however, prior art fluid sampling devices and methods have had the disadvantages of being relatively complex and of not obtaining a true representative sample due to contaminants in the fluid above the predetermined depth. U.S. Pat. Nos. 3,815,422 to Niskin, 3,892,130 to Winget et al, 4,037,477 to Niskin, and 4,050,315 to Markfelt and British Patent Nos. 566,752 and 1,107,180 are representative of prior art fluid sampling devices operable to obtain fluid samples at predetermined depths.